Method of detecting leakage in oil wells



A118 12,1947 N. G.'HAsELT|NE Erm. 2,425,531 METHOD 0F DETECTING LEAKAGE 1N on.. wFLLs.`

' Filed sept. (so, `1944 lected in separate storage systems.

'Patented Aug. 12, 1947 UNITED STATES METHOD OF DETECTING LEAKAGE IN OIL WELLS Nathaniel G. Haseltine and Morris Bock, Dallas, Y 7'/ Tex., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application September 30, 1944, Serial No. 556,508

7 Claims.

'I'he present invention relates in general to oil vwell production andvparticularly to the producmon practice to produce oil from more than one l horizon through a single Well. In such cases it is generally desirable or necessary for various reasons that the oil be withdrawn as a separate stream from each horizon and-that it be colis that the properties of crude oils from different zones may be suiciently different to make their pressure for each horizon may be exercised.

'Furthermore, in many cases government regulations fix the allowable production from each zone and prohibit production from separate zones through the same string of tubing. lAgain,

certain legal questions such asrights of royalty interests may be involved, necessitating separate y production from each horizon.

.The separate withdrawal of oil from two pro- One reason 15 detected by observing changes in the absorption characteristics of the oil for light radiation having a wave length above a certain value, It

has been discovered that, whereas oils from different horizons of a given eld all. have substantially the same absorption .characteristics for light radiation of wave length below about 5500 Angstroms, such oils differ substantially in absorption characteristics when the wave length is above the aforesaid value. it has been found that there is a marked tendency for the oil Within a single productive zone not to exhibit a real variation in these absorption characteristics to any large lextent, although, in some cases, there may be a minor amount of such variation. Accordingly, by subjecting samplesoi the oil, as production from the well proceeds, to suitable spectroscopic tests employing light radiation of wave length above 5500 Angstroms, andthen comparing the results with predetermined absorption characteristics obtained under similar conditions for the uncontaminated oil and noting any substantial change in these characteristics, contamination of oil of one horizon by that of another is readily indicated.-

In testing the oil to determine its absorption characteristicsior, from another viewpointits transmission characteristics), a spectrophotometer or absorptio'meter is employed. Instruductive zones through a single Well generally has ments of this kind are well known and generbeen accomplished by setting a packer in the annular space between the tubing and casing to/A seal off the two zones andl then allowing the Well y`to produce from the lower zone through the `tubing while permitting it to produce from the upper zone through lthe annular space. vHowever, it has been found in actual practice that l dililiculty often is encountered in getting a permanent seal between the two productive zones,

and it is not uncommon that leakage of oil from the zone of higher pressure to the lower pressure zone develops, Whenever such contamination of oil of one zone by that of another occurs, it is desirable that it be detected in order that proper preventive measures may be taken without delay. Accordingly, there is a need for a rapid and simple method of detecting such contamination. Several of the usual methods employed in testing crude oils have been'tried for this purpose but none of these has proved satisfactory.

For example, when'distillation tests were tried, they proved to :be not sufficiently diagnostic to detect contamination even of substantial degree and also to be more time consuming than desired for practical use.

The present invention provides a method of detecting contamination of oil from one horizon by that of another, whereby leakage of oil 'between horizons may readily be indicated. In

accordance with the invention, such leakage is 60 sults obtained by spectroscopic tests as applied.-.

,//ally comprise a source of light radiation, an optical system for separating the radiation into its constituent wave rlengths and for transmitting rays of the desired wave lengths through the sample, and means for measuring the intensity of .the radiation emerging from the sample. Some of these instruments are designed so that the wave length ofthe radiation passed into the sample may be varied over a desired range in order that the per cent transmission may be determined from veach wave lengthwithin the range. Such apparatus is described in an article appearing in "Industrial and Engineering Chemistry, analytical edition, volume 13, pages 667- 4b 754' (1'941), enuued Instrument methods of chemical analysis, particularly on pages 684- 692. Spectrophotometers of this type Vmay be used if desired, although, for the purposes of the invention, it is unnecessary that. the per cent transmission be determined at various wave lengths and it is suicient to make a' single determination using either monochromatic radiation or a radiation band of relatively Wide spectral range. |Spectrophot'ometers or absorptiometers which utilize a single restricted band of For the purpose of illustrating the. type otre- On the other hand,

, in the present invention,

there is .attached hereto a single sheet of drawings showing in graphical form the results of tests on oils made by means of a Hardy spectrophotometer (described in the previously referred to article). By means of this instrument, the 'per cent transmittance of monochromatic light over the spectral range of 4000-7000 Angstroms was, determined. 'Ihe curves shown in the drawing are for two oils (designated as A and B) derived from the same field but from dliferent horizons. as well as for several blends of the two oils. The relationships between per cent transmittance and wave length is `represented for oil A and for oil B by the upper and lower curves, respectively, while the intermediate curves represent the various blends.

A comparison of the curves shows clearly that there is no substantial difference in the absorption characteristics of the oils for light of wave length below about 500 Angstroms. Above this value, however, the curves diverge and the diiference in absorption characteristics becomes more pronounced as the wave length is increased. Thus,

at 7000 Angstroms there-is a very marked differ' ence in absorption characteristics. It is further to be noted, as indicated by a comparison of the curves for the blends with those of the uncontaminated oils taking into consideration the compositions of the blends, that the tests afford an approximation of the amount of contamination of oil from one' horizon by that of another.

l Although the data presented graphically in the drawing include wave lengths only up to '1000 Angstroms, it is to be understood that radia.

tions of still higher wave length may be used in accordance with the invention. In fact, in some cases it may be desirable to work at higher wave lengths in order to render the test method more sensitive in differentiating between oils. However, this has the drawback thatV` wave lengths greater than about 7000 Angstroms are outside of the visible light range and within the range of infrared radiation, so that more complicated and expensive instruments are required. From a practical aspect. it is generally preferable to work in the visible light range and preferably within a. range of about 6500-7000 Angstroms, but it is to be clearly understood that the invention is not necessarily limited to the range of visy ible radiation. I

.As evidence of the difference in absorption characteristics of oils from different horizons as well as of the substantial uniformity of oil within a given horizon, the following test data for various oil samples representing four productive horizons in one particular eld are illustrative. The tests were made with light radiation having a wave length of 7000 Angstroms. Each result listed represents a different well within the particular field, many of which were widely spaced throughout the field even for the same produc- Y ing zone.

Oil from zone B42, 4.2, 2.8, 2.6, 4.3 Oil from zone C66.7, 63.0

Oil from zone D9.6, 7.0, l8.5, 9.2, 7.7, 7.3,

- small.

`to aiord a comparison with the In practicing the invention, absorption characteristics for oils of the various horizons in question preferably are predetermined in order test results obtained as production proceeds. Uncontaminat' ed samples. representative of the various horizons, may be obtained in any suitable manner. one particularly reliable manner being to 'sample the flow streams of singly completed wells within the field. Before testing a sample, it is distinctly preferable to subject the sample to treatment adapted to remove water and sediment therefrom, since it has been found that such impurities may cause the test results to lbe inconsistent and unreliable. -For this purpose, either centrifugation or filtration serves as a particularly convenient and effective type of treatment.

In the case where two or more productive horizons are traversed by a bore hole and one vof the horizons is known to be under relatively low pressure, leakage to that horizon may be detected by observing substantial changes in the absorption characteristics as production proceeds, even in the absence of any absorption characteristic data for other horizons. However, this affords no indication of how much leakage is taking place. Accordingly it is generally preferable to know the absorption characteristics for oil of the other horizons or horizon so that the amount of leakage may be estimated. Since leakage cannot take place from a lower pressure zone to one of higher pressures, it is not essential in carrying out the invention that the oil from a higher pressure zone be tested as production proceeds, although at times it may be desirable to do so for the sake of following minor variations of absorption characteristics. Y

The invention is also useful even'in the absence of predetermined absorption characteristics. `In such cases, any initial leakage between productive horizons would not be detected. However, it has been found that leakage is apt to become progressively worse as production proceeds, so that, even though the actual absorption characteristics of uncontaminated oil of a. given horizon may not be known, it is possible to detect any substantial increase in the rate of leakage to that horizon by noting changes in the absorption characteristics of the oil stream withdrawn therefrom as the well continues to produce.

Having described oui invention, what we claim and desire to protect by Letters Patent is:

1. In the production of oil from a single bore hole traversing at least two productive horizons and in which leakage of oil from a horizon of higher pressure to one of lower pressure is apt to occur, the method of detecting such leakage as production proceeds which comprises determining the absorption characteristics of oil withdrawn during production from said lower pressure horizon for light radiation of wave length substantially above 5500 Angstroms and comparing the determined absorption characteristics with the absorption characteristics of oil previously withdrawn from said lower pressure horizon for light radiation of the same wave length. thereby to detect any substantial change in said characteristics as production proceeds and thus afford an indication as to whether leakage of oil from the higher pressure horizon to the lower pressure horizon has occurred.

2. The method defined in claim 1 wherein each of the said absorption characteristics are for light radiation of wave length within the range foi 6500-7000 Angstroms.

' hole traversing at least two productive horizons and in which leakage of oil from a horizon `of higher pressure to one of lower pressureis aptto occur, the method of detecting initial leakage as production is begun which comprises determining the4 absorption characteristics of oil withdrawn as production is begun from said lower pressure horizon for light radiation of wave length substantially above 5500 Angstroms and comparing the determined absorption characteristics with the absorption characteristics of uncontaminated oil from said lower pressure horizon for light radiation of the same wave length, thereby to detect any substantial difference in said characteristics as production is begun and thus afford an indicatjon of initial leakage between said horizons.

4. The method defined in claim wherein the4 said oil withdrawn during production and the said oil previously withdrawn are each subjected to treatment adapted lto remove water and sediment therefrom before being testedto determine the absorption characteristics.

5. In the production of oil from a singlebore hole which traverses a productive horizonv of lower pressure and a second productive horizon of higher pressure, and where, during the production of oil from said horizon of lower pressure, leakage of oil from the horizon of higher pressure to that of lower pressure is apt to occur, the method of detecting such leakage as production proceeds which comprises rst determining the absorption characteristics of oil withdrawn during production from said lower pressure horizon for light radiation of wave length substantially above 5500 Angstroms, determining the absorption characteristics of oil subsequently withdrawn' from said lower pressure horizon for light radiation of the same Wave length, and comparing the determined absorption characteristics of oil withdrawn from the same horizon under the two conditions to detect any substantial difference in the two determinations indicative of leakage of oil from the higher pressure horizon to the'lower pressure horizon.

6. In the production of oil from a single bore hole which traverses a productive horizon of lower pressure and a second productive horizon' of higher pressure, and where leakage of oil from the horizon ofhigher pressure to that of lower pressure is apt to occur,V the method of detecting such leakage as production proceeds which comprises determining the absorption characteristics of uncontaminated oil from said lower pressure horizon for light radiation of wave length substantially above 5500 Angstroms, and also determining the absorption characteristics of oil withdrawn from said lower pressure horizon during production from said single borehole for Alight radiation of the same wave length, and comparing the determined absorption characteristics to detect any substantial dierence in the two determinations indicative of leakage of oil from the higher pressure horizon to the lower pressure horizon.

7. In the production of oil from a single-.bore

hole traversing'at least two productive horizons and in which leakage of oil from a horizon-of higher pressure to' one of lower pressure is` apt to occur, the method of detecting such leakage as production proceeds which comprises determining the absorption characteristics of oil withdrawn during production from said lower pressure horizon for light radiation of wave length substantially above 5500 Angstroms, comparing the determined absorption characteristics with the absorption characteristics of uncontaminated `oil from said lower pressure horizon for light horizons, and also comparing the determined absorption characteristics with the rabsorption characteristics of uncontaminated oil from said higher pressure horizon for light radiation of the 1 I same wave length to thereby aiford an indication I of the amount of leakage between said horizons.

NATHANIEL G, HASELTINE.v MORRIS BooK.

REFERENCES CITED The following lreferences are of record in the file of this patent: y

UNrrED STATES PATENTS Hare Nov. 30, 

